When drilling is performed through several layers of material of different hardness it sometimes happens that the waste material from a relatively hard material damages the surface of a relatively softer material.
These problems may be minimised and eliminated by the provision of a micro-pecking mechanism. Micro-pecking means that the drilling is performed in a non-uniform manner, such that the drill spindle is advanced in pulses instead of being continuously fed. When the drill spindle is advanced in pulses the waste material that is machined away from the drill hole will be in the form of chips instead of long strips. The chips are easily removed by the rotation of the drilling implement without harming the surface of the produced drill hole.
A drilling tool with a micro-pecking arrangement is known from the patent specification FR 2952563 B1. In this arrangement the spindle is spring loaded in a first direction. Further, it comprises a rolling bearing with rolling elements that roll along an undulating rolling surface so as to periodically stress the spindle to move in a second direction opposite the direction of the spring. This arrangement causes an axial vibratory movement that accompanies the rotation that advances the spindle.
In some implementations it is not desired to have a vibratory movement. For instance it is not desired to have a vibratory movement when a countersinking is being machined to a work piece. Instead, it is desired to have a uniform advancement of the spindle such that the surface of the countersinking will be as uniform, i.e. as even, as possible. A vibratory movement would cause the surface of the countersinking to be undulated. Often, a drilling operation is combined with the machining of a countersinking.
Hence, there is a need of a drilling tool which may produce a vibratory or non-uniform advancement of the spindle at times when that is desired, but which may also be used to perform drilling with a uniform or non-vibratory advancement of the spindle at other times.